1. Field of the Invention
The present invention relates to a method for producing rare earth magnets as typified by neodymium magnets, in more detail, a method for producing nanocrystalline rare earth magnets having grains and grain boundary phases. Further, the present invention relates to nanocrystalline rare earth magnets having grains and grain boundary phases.
2. Description of Related Art
Rare earth magnets as typified by neodymium magnets (Nd2Fe14B) have been variously used as a very strong permanent magnet that is very high in magnetic flux density. In order to further improve the coercive force of the rare earth magnets, a grain is formed into a single domain particle having nano size (several tens to several hundreds nanometers).
Now, it is known that, in general sintered magnets (grain size of several micrometers or more), a heat treatment is applied after sintering to enhance the coercive force. In Japanese Patent Application Publication Nos. 6-207203 and 6-207204, for example, it is confirmed that when an aging heat treatment is applied to NdFeCoBGa system sintered magnets at a temperature equal to or less than the sintering temperature, the coercive force can be improved.
However, it was unknown whether the aging heat treatment is effective or not in magnets of which grains are formed into nano size. That is, while it is considered that the miniaturization of structure largely contributes in improvement of the coercive force, the heat treatment has a risk of making the grain size coarse. Accordingly, the aging heat treatment has not been applied on magnets in which grains have nano size.
In nanocrystalline rare earth magnets, it is very desirable to improve the coercive force. Accordingly, it has been strongly desired to establish an optimum method for improving the coercive force.